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MindCuber Troubleshooting Tips

Note: this page is under development...

This page includes a collection of questions, hints and tips intended to help you solve any problems you have with MindCuber. More will be added shortly.

Please read the General Tips before looking at a specific section to ensure that the most likely causes are eliminated first.

If after using this information you are still unable to resolve the issue, please leave a message on the MindCuber facebook page or on one of the MindCuber videos on YouTube describing the problem and what you have tried to resolve it.


  1. General Tips
  2. Scanning

1. General Tips

1.1 Build Instructions

This may seem obvious, but please check very carefully that MindCuber is built exactly as shown in the build instructions. There are several places where mistakes can easily be made that are difficult to spot. Some of them cause unexpected problems during operation.

Several common mistakes are described in later sections.

1.2 NXT Firmware Version

Check that the latest version of firmware, 1.31, is installed on the NXT.

If an earlier firmware version is installed, the MindCuber program may not run correctly because it requires functions that were not available in earlier versions or because of memory limitations.

The latest firmware is available from the Support section of the LEGO MINDSTORMS website.. Download this firmware to the NXT using the standard LEGO MINDSTORMS software.

1.3 Executable Program Version

Check that the correct variant and latest version of the executable program, MindCuber.rxe v2.0, has been downloaded to the NXT. (Note: the v2.0 here refers to the software version, not the NXT version)

If the wrong variant is used, the motors, in particular the turntable motor, will move incorrectly because the gear ratio is different between the two variants. The Rubik's Cube will not turn or tilt as required

The latest version also has improved color discrimination for the most reliable scan.

The variant and version of the program are displayed on the NXT screen as soon as the program is run.

The latest MindCuber.rxe for NXT 2.0 can be downloaded here

The latest MindCuber.rxe for NXT 8527 (orange box) or Education Base set can be downloaded here

(you may need to right click and select "Save link as..." depending on your browser)

1.4 Turntable Motor Alignment

When the MindCuber program is first run, the tilt arm and scan arm are moved automatically by the program to calibrate their positions. The turntable motor must be aligned manually.

Use the grey, left and right buttons on the NXT to carefully align the turntable motor when the program is running and waiting for a cube to be inserted. The motor should be aligned so that if the turntable is pushed gently by hand it will move sligtly and equally in each direction.

1.5 Batteries

Please try new or fully charged batteries in the NXT as several people have reported problems that disappeared when they replaced the batteries.

2. Scanning

MindCuber attempts to scan up to three times to try to determine the colors of the scrambled cube. If it fails, it will report either "Cube error" or "Scan error" at the end of the three attempts and flash the color sensor blue or red respectively.

2.1 Message "Cube error"

This indicates that the colors appear to be correct and in the right combination for the pieces expected on the puzzle. However, it suggests that the cube has been taken apart and put back together in a way that is impossible to solve only by turning faces.

A cube will be impossible to solve normally if one corner piece or one edge piece has been twisted or if two pieces have been exchanged. This can happen, for exampe if the cube is taken apart to adjust or lubricate it and put back together at random.

If this message is displayed, take the cube apart and put it back together completly solved. The scramble it by turning the faces of the cube as normal and try scanning again.

2.2 Message "Scan error"

Scanning may be unreliable for a number of reasons including:

2.3 Calibrate the Color Sensor

The color sensor is affected by a number of things such as lighting conditions and the color of the stickers on the cube.

It can be calibrated for specific conditions by performing the following:

  1. Solve the white face of the Rubik's Cube
  2. Stop the program
  3. Start the program and then immediately press the orange button again and hold it until the screen says "Calibrate white..."
  4. Insert the cube into the turntable with the white face upwards
  5. MindCuber will scan just the white face and then stop and display three numbers on the NXT display. It saves these numbers and uses them to calibrate the color sensor
  6. Remove the cube, scramble it and insert it again for a normal scan and solve


See more LEGO robot Rubik's Cube solvers at youtube.com/IAssemble

Copyright © 2013-2015 David Gilday

LEGO and MINDSTORMS are trademarks of the LEGO Group
Rubik's Cube is a trademark of Rubiks Brand Limited

Disclaimer: thoughts and opinions expressed here are my own